Field of the Invention
This invention relates to the use of low dose radiation sources to process shellfish (mollusks and Crustacea) on board ship. Investigations were conducted on the radiation preservation of shrimp using organoleptic, biochemical, and microbiological tests as indices of product quality.
This invention relates to a method for controlling and reducing populations of foodborne pathogens in shellfish using low dose sources of radiation on board ship.
This invention also relates to the design of a shipboard shellfish processing facility that will use machine generated electron beam technologies to decontaminate, disinfest and extend the shelf life of mollusks and crustacean shellfish by reducing or eliminating the spoilage microflora, e.g., pseudomonas, psychotrophic spoilage organisms, the vibrio, salmonella, listeria and Botulism spoilage microorganisms. These microorganisms, with the exception of botulism, are among the most radio-sensitive microbial species (Thornley, 1963).
Linear accelerators, usually call "linacs," are electric machines producing high energy electron beams. These electrons penetrate the products of some centimeters to 80 centimeters, according to the density of the product. The linear accelerators is composed of a control system, a modulator, a hyper-frequency generator, an accelerating section and a scanning device. The modulator, power-supplied by main power, sends pulses to the klystron which generates hyper-frequency waves. The hyper-frequency waves are injected in the accelerating section in the same time as electrons generated by an electron gun. The electrons are accelerated by an electric field created by hyper-frequency waves and reach an energy of 5-10 MeV. Electromagnetic radiation in this range of energy encompasses both X-Rays and Gamma Rays generated by machines possessing 5 MeV and 10 MeV particle energy capacities respectively. Electromagnetic radiation in this range of field power encompasses both x-ray and gamma rays generated by machines of 5 MeV and 10 MeV maximum field strength, respectively. The accelerated electron beam is scanned over the product, penetrates it and deposits its energy in order to sterilize, decontaminate or disinfect (U.S. Pat. No. 2,858,441--Gale and U.S. Pat. No. 2,729,748--Robinson). It is known that radio-pasturized or sanitized foodstuffs can be processed without flavor degradation by subjecting the product to an atmosphere of carbon dioxide under super atmospheric pressure and exposing the product to low or even high doses of radiation. Accordingly, it is the object of this invention to provide a simple and efficient process for irradiating shellfish on board ship while preventing the development of off flavors, discolorations and spoilage (U.S. Pat. No.3,483,005--Urbain, et al).
During the treatment, all operations parameters are controlled and recorded by a control computer. This process reduces computer computation time and identifies those essential variable which must be specified (design variables) in order to obtain a solution.
The following is a list of shellfish that may be effectively irradiated for vibrio and pseudomonas decontamination:
______________________________________ REQUIR- ED DOSES ______________________________________ MOLLUSC, BIVALVE MOLLUSC A. Clams 1. Soft-shelled clams (mya arenaria) 2 kGys 2. Surf clams (spisula solidissima) 2 Kgys B. Oysters 1. Gulf Oysters (crassosteria virginica) 2 kGy 2. Florida Oysters (crassosteria virginica) 1-2 Kgy 3. Pacific Oysters (crassosteria gifas) 1-2 kGy 4. Oysters (no species stated) 2 kGy C. Scallops 1. Sea Scallops (placopecten magellanicus) .75 kGy 2. Alaskan Scallops (pectren caurinus) CRUSTACEANS A. Crabs 1. Dungeness crabs (cancer Magister) 2-3 kGy 2. King crab (paralithodes camtschatica) 1-2 kGy 3. crabs (no species indicated) 1-2 kGy B. Lobsters 1. American lobster (Homarus americanus) 1 kGy 2. European lobster (Homarus gammarus) 1 kGy 3. Norwegian lobsters (Nephrops norvegicus) 1 kGy C. Shrimp 1. White shrimp (penacus setiferus) 1-2 kGy 2. Brown shrimp (homarus gammarus) 1.5 kGy 3. European brown shrimp (crangon vulgaris) 1.5 kGy 4. Pink shrimp (panaeus duorarum) 1-2 kGy 5. Shrimp (metapenaeus affinis, penaeus indicus 1-2 kGy and parapeneopsis stylifera) 6. Shrimp (no species indicated) 1-2 kGy ______________________________________
Headed, unshelled shrimp, for example, have been treated with one, two or three kGy on board ship; then placed on ice. Removal of the heads on shrimp before irradiation and depuration is recommended because tests have proven up to 75% of the bacteria are contained in the head. The shelf life of the product was ten to twenty days [(1) Novak, et al], a considerable extension of the storage life at refrigerator temperature above freezing. The energy requirements for freezing are greater than low dose treatments (Brynjolfsson, 1978). This would do away with the costs of freezing, storage and defrosting--resulting in ancillary energy savings. Since shrimp tend to deteriorate on board ship, the application of ionizing radiation to this product should preferably be carried out on ship [(3) and (4) Ronsivelli, et al].